This invention relates to the field of telephone equipment, and more particularly to the field of telephone test equipment.
The proliferation of subscriber-owned telephone equipment has raised a serious problem for telephone companies: in the event a subscriber reports a problem, the company will waste resources if it dispatches a service person to the subscriber location, only to learn that the problem originates in subscriber-owned equipment not provided by the company. Therefore, it would be highly advantageous for the telephone company to be able to determine quickly whether a reported problem arises in the telephone line or in the subscriber equipment.
The prior art gives little assistance to the telephone company in this situation. Most of the available art is directed to the situation in which a telephone installer needs to identify particular line pairs from among a plurality of lines, as when a service person in working on a multi-pair cable. In that situation, U.S. Pat. No. 3,427, 538, to Bohnenblust teaches an arrangement whereby a workman at a remote location could apply a probe to a selected cable pair; the central office would then apply a signal to each cable pair in sequence until the test tone was detected at the remote location. This apparatus verifies reception of the tone by comparing signals passed through a delay circuit, using a coincidence technique. A similar system is shown in U.S. Pat. No. 3,559,055, to Thompson, showing an arrangement whereby the test signal is validated by a pulse recurrence timer. Other approaches, including that a Collier, U.S. Pat. No. 3,628,138, which teaches identification of a particular line pair by employing a modulated Gaussian noise source on the line, all include the requirement that a service person be physically present at the subscriber location in order to practice the inventions.
Beerbaum, in U.S. Pat. No. 3,912,882, recognizes this problem and proposes a partial solution. That disclosure places an apparatus at the subscriber location, coupled to a single telephone line. When the central office desires to check a line, it transmits a tone on that line. The apparatus detects the tone and disconnects the customer terminal equipment so that the central office can perform a prescribed series of line tests. At the conclusion of the testing, the apparatus reconnects the subscriber equipment.
This teaching addresses the demonstrated need, but it does so inefficiently and expensively, it being limited to a single telephone line. Therefore, at a subscriber location having more than one line, such as the typical 25-line termination block, one such apparatus would be required for every line. Clearly, a need exists to utilize a single apparatus to service a plurality of lines. Moreover, Beerbaum's apparatus could not be adapted to a multi-line situation without serious disadvantage. This disclosure teaches that the check tone transmitted by the central office "must be in excess of about four seconds", and preferably is ten seconds. Therefore, the minimum time necessary to scan every line of a 25-pair termination block utilizing this apparatus would be 100 seconds, and preferably would be 250 seconds. This time is stated as being necessary in order to discriminate the check tone and other signals appearing on the line.
Thus, notwithstanding the gains made by the prior art, the industry remains in need of a method for identifying a particular telephone line from among a multi-pair grouping and isolating that line, efficiently and quickly.